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    Subject[RFC] [PATCH 2.6.37-rc5-tip 7/20] 7: uprobes: store/restore original instruction.

    On the first probe insertion, copy the original instruction and opcode.
    If multiple vmas map the same text area corresponding to an inode, we
    only need to copy the instruction just once.
    The copied instruction is further copied to a designated slot on probe
    hit. Its also used at the time of probe removal to restore the original
    instruction.
    opcode is used to analyze the instruction and determine the fixups.
    Determining fixups at probe hit time would result in doing the same
    operation on every probe hit. Hence Instruction analysis using the
    opcode is done at probe insertion time.

    Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    ---
    arch/Kconfig | 1 +
    kernel/uprobes.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++----
    2 files changed, 57 insertions(+), 5 deletions(-)

    diff --git a/arch/Kconfig b/arch/Kconfig
    index 6e8f26e..bba8108 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -65,6 +65,7 @@ config UPROBES
    bool "User-space probes (EXPERIMENTAL)"
    depends on ARCH_SUPPORTS_UPROBES
    depends on MMU
    + select MM_OWNER
    help
    Uprobes enables kernel subsystems to establish probepoints
    in user applications and execute handler functions when
    diff --git a/kernel/uprobes.c b/kernel/uprobes.c
    index 8a5da38..858ddb1 100644
    --- a/kernel/uprobes.c
    +++ b/kernel/uprobes.c
    @@ -448,21 +448,72 @@ static int del_consumer(struct uprobe *uprobe,
    return ret;
    }

    +static int copy_insn(struct task_struct *tsk, unsigned long vaddr,
    + struct uprobe *uprobe)
    +{
    + int len;
    +
    + len = uprobes_read_vm(tsk, (void __user *)vaddr, uprobe->insn,
    + MAX_UINSN_BYTES);
    + if (len < uprobe_opcode_sz) {
    + print_insert_fail(tsk, vaddr,
    + "error reading original instruction");
    + return -EINVAL;
    + }
    + memcpy(&uprobe->opcode, uprobe->insn, uprobe_opcode_sz);
    + if (is_bkpt_insn(uprobe)) {
    + print_insert_fail(tsk, vaddr,
    + "breakpoint instruction already exists");
    + return -EEXIST;
    + }
    + if (analyze_insn(tsk, uprobe)) {
    + print_insert_fail(tsk, vaddr,
    + "instruction type cannot be probed");
    + return -EINVAL;
    + }
    + uprobe->copy = 1;
    + return 0;
    +}
    +
    static int install_uprobe(struct mm_struct *mm, struct uprobe *uprobe)
    {
    - int ret = 0;
    + struct task_struct *tsk;
    + int ret = -EINVAL;

    - /*TODO: install breakpoint */
    - if (!ret)
    + get_task_struct(mm->owner);
    + tsk = mm->owner;
    + if (!tsk)
    + return ret;
    +
    + if (!uprobe->copy) {
    + ret = copy_insn(tsk, mm->uprobes_vaddr, uprobe);
    + if (ret)
    + goto put_return;
    + }
    +
    + ret = set_bkpt(tsk, mm->uprobes_vaddr);
    + if (ret < 0)
    + print_insert_fail(tsk, mm->uprobes_vaddr,
    + "failed to insert bkpt instruction");
    + else
    atomic_inc(&mm->uprobes_count);
    +
    +put_return:
    + put_task_struct(tsk);
    return ret;
    }

    static int remove_uprobe(struct mm_struct *mm, struct uprobe *uprobe)
    {
    - int ret = 0;
    + struct task_struct *tsk;
    + int ret;
    +
    + get_task_struct(mm->owner);
    + tsk = mm->owner;
    + if (!tsk)
    + return -EINVAL;

    - /*TODO: remove breakpoint */
    + ret = set_orig_insn(tsk, mm->uprobes_vaddr, true, uprobe);
    if (!ret)
    atomic_dec(&mm->uprobes_count);


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